# CVE-2026-74449: drm/amd/display: Fix divide-by-zero in calculate_mcache_setting on zero viewport

> A divide-by-zero error in the AMD display driver causes a kernel panic when processing a zero-area viewport, leading to system denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-74449, DEBIAN-CVE-2026-74449, GHSA-2qf4-qh24-m72c, UBUNTU-CVE-2026-74449

## What is CVE-2026-74449?

CVE-2026-74449 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix divide-by-zero in calculate_mcache_setting on zero viewport

If a plane reaches calculate_mcache_setting with a zero-area viewport,
calculate_mcache_setting exits early with num_mcaches == 0 and
mvmpg_width/height == 0. This will cause a divide-by-zero panic and can
also cause an underflow on num_mcaches.

Fix this by changing calculate_mcache_setting to bool and adding guards
after each calculate_mcache_row_bytes call. If num_mcaches or
mvmpg_width/height is zero, return a false. Callers will propagate the
failure as a rejected mode, which prevents the panic.

(cherry picked from commit 29c0f7c655f47bcbd575ff75e58480df6ec3c9da)

## Which versions are affected by CVE-2026-74449?


## How do I fix CVE-2026-74449?

Apply the vendor's patch.

## Is CVE-2026-74449 being exploited?

There is no known exploitation of CVE-2026-74449 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74449 and fix it if it is affected.

What it is: CVE-2026-74449 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74449 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74449/ (Markdown: https://insights.sbomify.com/CVE-2026-74449/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74449
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74449
- OSV: https://osv.dev/vulnerability/CVE-2026-74449

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74449/
Summaries are generated and may contain mistakes; the official description above is the record.